What is the significance of asymmetry on a craniocaudal (CC) view in a mammogram?

Mammographic Asymmetry on CC View: Clinical Significance and Management

Asymmetry on a craniocaudal (CC) mammographic view requires diagnostic workup with additional imaging views and targeted ultrasound, as it may represent underlying malignancy including ductal carcinoma in situ (DCIS) or invasive cancer, though most cases are benign. 1, 2

Diagnostic Significance

Asymmetry or focal asymmetry on mammography can represent several pathologic entities:

• Malignant lesions: DCIS presents as asymmetry/focal asymmetry in a minority of cases (more commonly seen as microcalcifications), while invasive carcinomas frequently manifest as asymmetries with various margin characteristics 1
• Benign lesions: Intraductal papillomas may appear as asymmetrically dilated ducts or circumscribed subareolar masses 1
• Sensitivity limitations: Mammography alone has relatively low sensitivity (15%-68%) for detecting malignancy in symptomatic presentations, with specificity ranging 38%-98% 1

Recommended Diagnostic Algorithm

Initial Imaging Workup

Perform diagnostic mammography with additional views immediately 2:

• Spot compression views: Essential to determine if the asymmetry persists or represents summation artifact 1, 2
• Magnification views: Particularly helpful for evaluating any associated microcalcifications 2
• Targeted ultrasound: Should be performed concurrently to evaluate the area of concern 2

BI-RADS Assessment and Follow-Up

For BI-RADS 1-3 (Negative, Benign, or Probably Benign) 2:

• Clinical re-examination in 3-6 months 2
• Follow-up imaging with diagnostic mammogram and/or ultrasound every 6-12 months for 1-2 years to assess stability 2
• Return to routine screening if stable 2

For BI-RADS 4-5 (Suspicious or Highly Suggestive of Malignancy) 2:

• Tissue biopsy is mandatory using core needle biopsy (preferred method) or needle localization excisional biopsy 2
• Ultrasound guidance for biopsy when lesion is sonographically visible 1

Clinical Context Considerations

In Pathologic Nipple Discharge

When asymmetry is identified in patients presenting with pathologic nipple discharge:

• The finding warrants additional spot compression and magnification views of the subareolar region 1
• Risk of underlying malignancy is elevated (3%-29% of pathologic nipple discharge cases) 1
• Negative mammography has high negative predictive value (88%-90%), but low sensitivity (10%-26%) for malignancy and high-risk lesions 1

Performance Characteristics

Important limitations to recognize 1:

• Positive predictive value of mammography for malignancy: 18%-42%
• Negative predictive value: 88%-90%
• Small lesions, purely intraductal lesions, or those without calcifications may not be visible on mammography despite being malignant 1

Critical Pitfalls to Avoid

• Never dismiss asymmetry without additional views: Summation artifact must be excluded with spot compression before reassurance 1, 2
• Do not rely on mammography alone: Ultrasound identifies additional lesions not visible on mammography in 63%-69% of symptomatic cases 1
• Ensure appropriate follow-up: Even with negative additional imaging (BI-RADS 3), short-interval follow-up for 1-2 years is necessary to confirm stability 2
• Recognize that normal mammography does not exclude malignancy: The sensitivity is limited, particularly for small or purely intraductal lesions 1